This study will examine in detail the ionic selectivity of acetylcholine-activated postsynaptic channels in neurons of the autonomic ganglia of amphibia. Particular attention will be focused on the channels' permeability to various foreign cationic organic amines that have different sizes, shapes, and hydrogen bonding characteristics. The purpose of this study is two-fold: 1. To elucidate the molecular morphology of neuronal synaptic channels; 2. To explore the possiblity of using radioactively-labeled amines to tag neurons that take up the label as a consequence of synaptic activity. Two different experimental approaches will be employed in this investigation: 1. Electrophysiological studies using intracellular recording techniques; 2. Measurements of transmitter-induced uptake of radioactively labeled materials into neurons. Autoradiography will be used to identify individual neurons that have been functionally tagged. This tagging technique would allow one to measure the functional activity of a neuron without the use of microelectrodes and would have wide application in studies of other synapses.